In digital communication networks, transmission services of multimedia data, e.g. music download services, video streaming services and TV over Internet Protocol (IPTV) services are increasingly offered and used.
Subscribers to such services can download digital content, e.g. media data like audio, 3D-audio, video or 3D video files to corresponding user terminals, e.g. to mobile phones, computers or television receivers. Without an efficient measure of protection, digital data can be extensively used by any recipient, e.g. being copied, modified and/or distributed to arbitrary further recipients. The content providers however want to restrict the use of the distributed multimedia data. One technical option is the use of Digital Rights Management (DRM) technologies as e.g. being defined by the Open Mobile Alliance (OMA) that is a standardization body in the field of mobile communication, addressing controlling content being transmitted within mobile networks, e.g. preventing downloaded content from being forwarded or copied to further users.
An alternative solution for protecting from unauthorized use of transmitted content can be derived by applying so-called (digital) watermarking denoting technologies to embed information robustly and imperceptibly into the multimedia data. The term watermark refers to well-known techniques marking paper by placing recognizable images or patterns into the paper. Watermarking does not prevent copying or distribution, but it allows e.g. identifying individual versions of the multimedia data, and therewith identifying users that provide unauthorized copies to further recipients. A general description of watermarking technologies can be gathered e.g. from the article “Multimedia Watermarking Techniques”, Proceedings of the IEEE, vol. 87, no. 7, pp. 1079-1107, July 1999 of F. Hartung and M. Kutter.
Watermark encoding however might be computationally complex and time-consuming, especially if a large amount of data to be watermarked, e.g. the data of a digital video stream. Thus, watermarking is preferably done centrally at a powerful network node of a corresponding internet service provider's network. Central watermarking however means that a plurality of differently marked multimedia signals have to be distributed from a server of an internet service provider over suitable nodes of an access network to a corresponding plurality of end user terminals. Such suitable nodes might comprise so-called Digital Subscriber Line Access Multiplexers (DSLAM) connecting multiple customer Digital Subscriber Lines (DSL) to a high-speed backbone line using multiplexing techniques, and so-called broadband remote access server (BRAS) aggregating user sessions from the access network, thereby routing traffic to and from the digital subscriber line access multiplexers (DSLAM) on an Internet service provider's (ISP) network.
If the watermarked signals are generated in the core network, a plurality of copies of the multimedia stream needs to be transmitted, as watermarked signals are to be individual for each user (in other words, it is not possible to apply multicast or broadcast techniques for gaining transmission resources). However, the bandwidth available for a broadband provision of multimedia streams across a network is a scarce resource.